Realist Synthesis of the International Theory and Evidence on Strategies to Improve Childhood Vaccination in Low- and Middle-Income Countries: Developing Strategies for the Nigerian Healthcare System

Background Childhood vaccination coverage rates in low- and middle-income countries (LMICs) vary significantly, with some countries achieving higher rates than others. Several attempts have been made in Nigeria to achieve universal vaccination coverage but with limited success. This study aimed to analyse strategies used to improve childhood vaccine access and uptake in LMICs in order to inform strategy development for the Nigerian healthcare system.   Methods A realist synthesis approach was adopted in order to elucidate the contexts and mechanisms wherewith these strategies achieved their aim (or not). Nine databases were searched for relevant articles and 27 articles were included in the study. Programme theories were generated from the included articles, and data extraction was carried out paying particular attention to context, mechanism and outcomes configurations.   Results Interventions used in LMICs to improve vaccination coverage were categorised as follows: communication/ educational, reminder-type, incentives, social mobilisation, provider-directed strategies, health service integration and multi-pronged strategies. The strategies that appeared most likely to be effective in the health contexts of contemporary Nigeria include communication and educational interventions; employing informal change agents, and; monitoring and evaluation to strengthen communication. The programme theories for the use of reminders, social mobilisation, staff training and supportive supervision were observed in practice, and these strategies were generally successful within some contexts. By contrast, the use of monetary incentives in Nigeria is not supported by the evidence, although further research and evaluation is required. The integration of other interventions with routine immunisation (RI) to improve uptake was more effective when the perceived value of the other program was high. Adoption of multipronged interventions for hard to reach communities was beneficial. However, caution should be exercised because of varying levels of published evidence in respect of each intervention type and a relative lack of the rich description required to conduct a full realist analysis.   Conclusion This paper adds to the evidence base on the adaption of strategies to improve vaccine access and uptake to the context of LMICs.